The pain on the outside of the breast after milking is considered to be caused by breast stimulation, breast hyperplasia, mastitis, and so on. 1. Breast stimulation: because the milk itself will cause some stimulation to the breast, which will lead to pain, after milking, lactin will still cause stimulation to the breast, causing a slight sting. 2. Mammary gland hyperplasia: mainly because during the breastfeeding period, the body’s estrogen and progesterone levels rise, which will cause stimulation of the mammary glands, resulting in mammary gland hyperplasia will cause slight pain in the breasts. 3. Mastitis: If the milk ducts can not be unblocked in time or secondary infection, it is easy to trigger inflammation of the mammary gland, resulting in breast pain, and most of them will be accompanied by red, swollen and hot pain in the breast. The pain on the outside of the breast may also be caused by other reasons such as trauma caused by squeezing, it is recommended to go to the hospital in time, after clarifying the cause, targeted treatment or treatment.